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A239208
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Numbers n such that sigma(n) divides the sum of the numbers x not coprime to n, with x<=n.
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2
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18, 135, 891, 4095, 10560, 13120, 14144, 21600, 23199, 74655, 144495, 192311, 404415, 4197375, 4612608, 5675775, 6664680, 9180800, 10953215, 11110400, 14381055, 18162144, 18420480, 18920000, 20765024, 25159680, 32058351, 41055200, 55889920, 65327104, 65982464
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OFFSET
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1,1
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COMMENTS
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Numbers n such that sigma(n) | n/2(n+1-phi(n)).
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LINKS
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EXAMPLE
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18/2*(19-phi(18)) = 117, sigma(18) = 39 and 117 / 39 = 3.
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MAPLE
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with(numtheory); P:=proc(q) local a, n;
for n from 1 to q do a:=n/2*(n+1-phi(n)); if type(a/sigma(n), integer) then print(n);
fi; od; end: P(10^6);
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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